Police will investigate an incident which prompted the evacuation of a building on Oxford Street, in Sydney’s CBD, after officers wearing bullet-proof vests spent several hours searching the building without finding anything.

Police began a search of an office building in Darlinghurst after they received information about 4:40pm.

The ABC understands that police wearing bullet-proof vests searched the 10th floor of a 23-storey building.

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Police emphasised that there was no evidence it was a terrorism-related incident.

They later issued a statement saying the search was complete and nothing was found.

Some minor traffic closures were put in place and traffic was delayed after workers were evacuated.

A witness who works on the building’s sixth floor said there were no evacuation alarms, but when employees went downstairs to the foyer police told them to leave the area.

“We honestly had no idea what was going on. We looked through our windows and most of what we could view of our building was surrounded by cop cars and cop vans,” she said.

“And it was at that point they were starting to tape up around the building, and we realised it was sort of getting serious.”

The witness also said one police officer told them there were reports a man had a gun.

“As we walked out of the building into the lobby, my boss tried to ask one of the police officers, you know, ‘what’s going on’, and they didn’t want to comment,” she said.

“And as we exited the building we saw another cop and we questioned him and he said ‘look, there’s a guy in the building suspected to be armed with a gun’.